Typically, bolts are used for the assembly of two or more unthreaded objects (e.g., panels, wooden boards, drywall, etc.) with the aid of a nut. To couple two object, each object includes a hole and the bolt is inserted through the holes in each of the objects. The holes are formed to have the approximate diameter as that of the shaft of the bolt. Then, the nut is coupled to the end of the shaft of the bolt that is exposed to the outside of the second object and is fastened, allowing the first object to be coupled with the second object as a single body.
With such a conventional coupling structure, work may be done only when a worker can access both the bolt and the nut when coupling the two objects. However, in some work environments, the worker may not be able to access the outside of each object with his hand or tool. In this case, fastening devices such as bolts and nuts cannot be used.